1. Technical Field
The invention concerns a turbine flowmeter for measuring the consumption of fluids, especially water, which comprises a housing with an intake, a discharge, and a flow tube; a counter for measuring and indicating the consumption; a turbine in the flow tube with a hub, a number of radial vanes mounted on the hub, and a more or less hemispherical front that faces the fluid flow; a holding insert, which consists of a water guide cross, which comprises a hub, radial struts that extend from the hub to the wall of the flow tube, a nozzle head that surrounds the front of the turbine, leaving a gap through which the fluid flows, and a central opening in the nozzle head, and which (holding insert) further consists of an insert base body, which comprises a hub and radial struts that extend from the hub to the wall of the flow tube; and a device that detects the revolutions of the turbine and transmits them to the counter.
2. Prior Art
RU 2082102 C1 describes the principle of a turbine flowmeter, whose turbine rotates freely suspended, i.e., without mechanical support, behind a nozzle head inserted in the fluid flow that is to be measured. The revolutions of the turbine are read out by electromagnetic means. The great advantage of this design is the complete elimination of mechanical support of the turbine, since the turbine rotates completely without contact, which is achieved by the clever use of the fluid flow acceleration that takes place in the nozzle head and the associated reduction of the pressure in the fluid.
Unfortunately, this design also has significant practical disadvantages. For one thing, trouble-free electromagnetic transmission of the rotational speed is often not possible, especially when the flowmeter housing, as is generally the case and as is necessary when high line pressures are involved, is made of steel or cast steel. For another, the suspension principle works only when the fluid has attained a certain minimum flow velocity. If the flow velocity is zero or close to zero, the position of the turbine is completely undefined. At a flow velocity that is slowly increasing from zero, the turbine is carried along by the flow and thus loses the optimum position behind the nozzle head that is necessary for the suspension principle. As a result, measurement at low volume flow rates is not guaranteed.
U.S. Pat. No. 2,709,366 discloses a similar turbine flowmeter. It has a shaft that is rigidly mounted in the center of the flow tube. The elongated turbine is furnished with two bearings and rotates on this shaft. The downstream end of the turbine is expanded. Before this expansion, there is a complementary constriction of the flow tube. This results in the formation of a gap, in which the entire fluid flow is accelerated. The resulting pressure reduction provides for the axial positioning of the turbine. Of course, the gap is very short, so that the positioning occurs only at large volume flow rates but does not occur at normal volume flow rates.
One disadvantage, however, is that the turbine has a central bore for the shaft. Due to the difference in the pressures upstream and downstream of the turbine, a portion of the fluid is drawn through this central bore. This can result in the deposition of suspended substances and minerals dissolved in the fluid, e.g., lime and magnesium. These deposits will brake the turbine, especially at low volume flow rates.
A common feature of turbine flowmeters is the mechanical transmission of the turbine revolutions to a counter. For WP turbine models, the gears used for this purpose must deflect the direction of rotation by 90°. Therefore, worm gears are generally used for this purpose, since they not only produce the desired deflection but at the same time reduce the high revolutions of the turbine to a level that can be tolerated by the counter. However, worm gears have high friction, because the gear wheels slide on each other. This also reduces the measuring sensitivity at low volume flow rates.